1. Field of the Invention
This invention relates generally to antenna feed assemblies and, more particularly, to antenna feed assemblies adapted to detect incident electromagnetic signals in two or more distinct frequency bands, simultaneously.
2. Description of the Related Art
With the recent growth in numbers of communication satellites in orbiting operation around the earth, the number of receiving stations has grown explosively. Each of these receiving stations requires an antenna capable of detecting signals at levels in the range of -120 dbm to -30 dbm, while rejecting terrestrial interference, and capable of polarization control. It is desirable for maximum utility that a single feed assembly exhibit the capability of operating simultaneously in two different frequency bands, e.g., the C band of 3.7 to 4.2 GHz and the Ku band of 11.7 to 12.2 GHz or the optional Ku band of 10.95 to 11.7 GHz. Simultaneous operation in yet a third frequency band, e.g., the S band of 2.544 to 2.655 GHz, also is desirable in many applications. A separate probe ordinarily must be provided for detecting signals in each band. This invention relates generally to microwave feed assemblies and, more particularly, to microwave feed assemblies that are adapted to detect signals in multiple distinct frequency bands.
It is desirable for multiple frequency feed assemblies to have the axes of their probes coaxial with a common reflector, to maximize the received signal strength at each frequency and to minimize unwanted side lobes. Coaxial mounting of dual frequency feeds without cross coupling and interference has not previously been effectively achieved. Studies have been made of input mismatches developed in TE11 mode coaxial feeds as well as the use of irises and their effects in coaxial waveguides. These studies, while helpful, have not given clear guidance for the design of an optimum dual frequency band coaxial feed assembly.
One attempt at a coaxial C- and Ku-band receiver antenna employs a plurality of wires surrounding a Ku-band assembly to bypass it as an obstruction and introduce the received signal into a C-band polarizer behind the Ku-band assembly. A common servo motor rotates both the Ku-band and C-band probes, to controllably adjust their polarities.
There is a need for a microwave feed assembly that can operate effectively to detect signals received from a common reflector in two or more frequency bands, with high signal strength and little unwanted side lobes. The present invention fulfills this need.